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Maybe John Lennon was onto something when he wrote those words
for the Beatles' song "Tomorrow Never Knows."

It turns out that that reality and imagination flow in different
directions in the brain, researchers say. The visual information
from real events that the eyes see flows "up" from the brain's
occipital lobe to the parietal lobe, but imagined
images flow "down" from the parietal to the occipital.

"There seems to be a lot in our brains and animal brains that is
directional — that
neural signals move in a particular direction, then stop, and
start somewhere else," said Dr. Giulio Tononi, a psychiatry
professor and neuroscientist at the University of
Wisconsin-Madison and one of the study's co-authors. "I think
this is really a new theme that had not been explored."

The finding, published in the November issue of the journal
NeuroImage, may lead to a better understanding of how the brain
processes short-term memories and how memory is connected to
imagination, the researchers said.

The occipital lobe sits in the lower, back part of the brain.
Containing the visual cortex, this lobe's primary function is to
process visual information. The parietal lobe lies above the
occipital lobe, and its primary function is to integrate sensory
information, such as vision, but also touch and sound. In doing
so, the parietal lobe assembles elementary building bricks from
so-called "lower-order" brain regions to create concepts, said
Daniela Dentico, a researcher at the University of
Wisconsin-Madison and lead author on the report.

A leading theory in
image processing "posits that our visual mental images are
not stored somewhere in the brain, but get actively
reconstructed," Dentico told Live Science. The brain does this,
she said, by reversing the order it uses for visual perception.
She described this as the "top-down" direction, which starts from
the big concept and moves back toward the smaller elements.

"Our study represents the first direct measure of the prevalence
of top-down signal flow during imagery," Dentico added.

To determine the flow of neural firing, the Madison researchers,
along with scientists at University of Liege in Belgium, asked
study participants who were hooked up to an
electroencephalography (EEG) machine to watch videos or to
imagine fantastical scenes, such as traveling on a magic bicycle.
EEG is an established technique that uses sensors on the scalp to
measure underlying electrical activity.

But because the brain isn't "quiet," EEGs tend to reveal the
cacophony of brain activity, said Barry Van Veen, a professor of
electrical and computer engineering at Madison and senior author
on the report.

So, to zero in on the flow of reality and imagination, the
researchers created complex statistical modeling requiring
high-throughput computing. From this, they could determine, for
the first time, the average directional flow of neural firing
during the tasks of seeing and imagining.

The researchers could not determine, however, whether imagination
originates in the parietal lobe. It may instead flow through the
parietal lobe from the frontal lobe, the brain region most
associated with human
intelligence. This is a topic for further investigation, the
researchers said.